Typically, wet, multicell, lead-acid SLI storage batteries include an open-topped, rectangular-shaped container sealed by a cover assembly, both of which are formed from an injection molded thermoplastic polymer, such as polypropylene. The container and cover have partition walls dividing the space within the battery into a plurality of substantially isolated cell cavities. Each cell cavity contains an electrode stack immersed in electrolyte. The cover typically defines a plurality of generally cylindrically shaped process holes, one associated with each cell cavity, through which the cell cavities are initially filled with electrolyte. In maintenance batteries, the process holes are closed-off by plugs which can be removed so that electrolyte can be periodically added through the process holes as maintenance is required.
Especially during charging, lead-acid storage batteries generate various gases in the cell cavities during operation, including hydrogen and oxygen. Hydrogen/oxygen mixtures can be volatile, creating an obvious potential for explosion. In recombinant lead-acid batteries, hydrogen and oxygen gas is retained in large part in the battery and induced to recombine into water. In wet lead-acid storage batteries, however, such gases are allowed to escape from the cell cavity and ultimately pass out of the battery through a venting system.
Wet, lead-acid storage batteries are used in a tremendous variety of vehicles and applications. As a result, such batteries are often subject to extreme and harsh operating environments. For example, batteries used in land moving vehicles, such as bulldozers, are frequently tilted at severe angles, as well as being subjected to intense operating vibrations. Thus, electrolyte can splash about the interior of a battery during normal battery use, as well as during installation and shipment.
There are a wide variety of known venting systems for expelling the volatile gases generated within a wet battery to the external, ambient space. The electrochemical performance of the battery may suffer, however, if electrolyte leaks from the battery. Accordingly, in general, venting systems in wet lead-acid batteries are directed to achieving a dual purpose: allowing gases to vent from within the battery, while retaining the electrolyte fluid therein.
Venting systems typically utilize venting plugs adapted for insertion within each process hole. A baffle positioned within the venting plug allows the passage of gases from the cell cavity while retarding the passage of electrolyte. Vent plugs are typically molded from a relatively rigid polymer, such as polypropylene, in molds that generally include vertical parting lines. As a result, the vent plugs often exhibit imperfect surfaces along the mold parting lines. These seams or excess flashing along the vertical surfaces of a vent plug can result in channels through which acid can leak due to both capillary action and the pressure developed during battery usage.
Positioned between the venting plug and the process hole is a seal or gasket, which is designed to provide a seal that prevents passage of gases and liquid between the plug and process hole. Vent plugs frequently utilize a separate seal or gasket, which is placed over the end of the plug body. Such gaskets are typically formed from die cutting molded sheet stock or by cutting molded tubes of rubber. Unfortunately, however, the vertical seam lines and flashing that can result from the vent plug molding process can prevent or inhibit the proper desired sealing operation of such separate gaskets. This is particularly true where the gasket is made of a relatively hard rubber.
U.S. Pat. No. 5,422,199 to Adams et al. discloses an integrally molded annular bead, which serves as the seal between the plug and the process hole, a single material being used for both the plug body and the bead. Unfortunately, this design can exhibit poor sealing characteristics and be prone to leakage along the seam or flashing line inasmuch as polypropylene is relatively non-resilient.
Despite the continuing effort in this area there remains a need for vent plugs that efficiently retain electrolyte within the cell cavity while effectively venting gases in a relatively safe manner, and which can be easily and economically manufactured.
Accordingly, it is a primary object of the present invention to provide a vent plug that is easily and economically manufactured. It is a related object to provide a vent plug that minimizes fabrication and assembly costs, while providing a consistent, reliable venting device.
A more specific object of the invention is to provide a vent plug that provides or facilitates an effective seal between the vent body and container cover.
It also is an object to provide a battery that vents gases generated with the cell cavities in a safe and efficient manner.
Another object of the present invention is to provide a battery having a venting system that minimizes the escape of electrolyte.
Yet another object is to provide a battery wherein all of the above advantages are realized.
These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.